1. Field of the Invention
This invention relates to a coupling mechanism, more particularly to a coupling mechanism for interconnecting a rotatable connecting end of a support on a broaching machine and a bit holder.
2. Description of the Related Art
FIGS. 1 and 2 show a conventional coupling mechanism for interconnecting a rotatable connecting end 151 of a support 15 and a bit holder on a broaching machine. The bit holder includes a rotary hollow shaft 10 that is rotatable by means of a motor 11, and a mandrel 13 that is rotatable with the hollow shaft 10 and that is slidable axially in a central axial hole 101 of the hollow shaft 10. The conventional coupling mechanism includes a first coupling member 20 and a second coupling member 30. The first coupling member 20 has a first disk part 22 and a neck part 21 having a cross-section smaller than that of the first disk part 22. The neck part 21 is adapted to be connected to the connecting end 151 of the support 15. The first disk part 21 is formed with a bore 23 and an internal thread 231 that engages the connecting end 151 of the support 15. The first disk part 22 has a plurality of slide holes 221 adjacent to the neck part 21, and a plurality of fastening holes 222 adjacent to the periphery of the first disk part 22. A plurality of first screw fasteners 24 extend through the fastening holes 222 and engage threaded holes 102 formed in the top face of the hollow shaft 10 in order to fix the first coupling member 20 on the hollow shaft 10. The second coupling member 30 has a second disk member 33 and a plurality of posts 32 projecting axially and upwardly from the second disk member 33. The second disk member 33 is slidable axially and is rotatable in the central axial hole 101 of the hollow shaft 10, and has therein an internal threaded hole 331 for engaging threadedly the mandrel 13. The posts 32 extend through the slide holes 221 and are connected to a ring 34 by second screw fasteners 35. The ring 34 is sleeved on the neck part 21. With the construction as such, the second coupling member 30 is slidable axially relative to the first coupling member 20 and is rotatable with the same. A hydraulic driving device 14 is provided adjacent to the support 15 for pushing the posts 32 of the second coupling member 30 and the mandrel 13 downwardly. Accordingly, the lower end 16 of the mandrel 13 can actuate a chuck 17 mounted on the lower end of the hollow shaft 10 so as to release a bit (not shown) from the chuck 17.
A disadvantage of such a conventional coupling mechanism resides in that when a hollow shaft 10 of a relatively small diameter is to be connected to the first coupling member 20, the diameter of the first disk member 22 is relatively small while the diameters of the neck part 21 and the connecting end 151 of the support 15 are maintained constant. Therefore, the structural strength of the first disk member 22 in which the slide holes 221 and the fastening holes 222 are formed is very weak.